Streptococcus hepaticus sp. nov. isolated from the liver of domestic pigs (Sus scrofa domesticus)

A Gram-positive coccus-shaped bacterium, which could not be identified by classical determinative bacteriology approaches, was isolated from the liver of two pigs in the United Kingdom. Initial testing based on cellular morphology and biochemical characteristics tentatively assigned the isolates to the genus <i>Streptococcus</i> but did not match any previously described species. The analysis of the 16S rRNA sequence determined that the isolates were most closely related to <i>Streptococcus gallinaceus</i> (98.6% identity). Analysis of three further housekeeping genes frequently applied in streptococcal taxonomy, <i>groEL</i>, <i>sodA</i> and <i>rpoB</i>, and a comparison against available type strain sequences confirmed that the isolates were most similar to <i>S. gallinaceus</i> in all cases (84.3%, 86.9% and 90.2% identity, respectively). The comparison of the average nucleotide identity (ANI) and <i>in silico</i> DNA-DNA hybridization values demonstrated that the novel species was distinct from other streptococcal species. Pairwise ANI values revealed that the two studied strains shared a pairwise ANI of 99.25% but were clearly distinct from previously described <i>Streptococcus</i> species (ANI ≤81.1% - best match <i>S. gallinaceus</i>). The taxonomic analysis described confirmed that the two strains represent a novel <i>Streptococcus</i> species for which the name <i>Streptococcus hepaticus</i> sp. nov. is suggested, with strain 20-1249^T (=NCTC 15092^T=LMG 33498^T) as the type strain.